GS Engineering & Construction Co., a major South Korean builder, said Friday that its first-quarter operating profit jumped to more than six times its profit a year earlier.

For the three months ending March 31, the company reported 380.4 billion won (US$356 million) in profits, up from 59 billion won the previous year, the company said in a statement.

The sharp jump in operating profit was driven by steady and solid gains in housing projects and one-off gains worth 180 billion won from its overseas plant planning business, a company spokesman said by phone.

"Some clients demanded changes in the planning of plants they ordered from GS E&C, and their additional payments for the changed orders were reflected in the first quarter results," he said.

The company said it expects such additional one-off income will continue to be factored into its bottom line this year.

Sales rose 15 percent to over 3.1 trillion won from 2.7 trillion won in the same period last year, the statement said.

The company's quarterly net profit figure and other earnings details will be released later this month, the spokesman said.